The reconstruction of the breast following ablative surgery has become an increasingly frequent surgical procedure. The development and use of silicone-gel and saline-filled silastic implants have contributed to the increased frequency of this procedure. Thickening and contracture of the fibrous capsule surrounding the silastic implant, however, remains a major post-surgical problem. Animal studies, as well as histologic evaluation of human capsule segments, have revealed the nature of this fibroproliferative response. Leakage or "bleeding" of silicone gel from silastic breast implants appears to be a major cause of this inflammatory response, which ultimately results in a constrictive fibrosis surrounding the silicone-gel implant. The use of "double-lumen" prostheses, with the outer chamber containing saline, decreases the inflammatory response initially but does not eliminate the ultimate fibroproliferative response. This application describes breast prostheses which contain less reactive, more biocompatible filling substances. The use of such breast prostheses will limit and control thickening and contracture of the fibrous capsule surrounding the prosthesis.